The folk at the Treasury have obviously been taking the Beatles's number When I'm 64 to their mandarin hearts. Anyone of that age - or who celebrates their 64th birthday between now and April 5 - is certainly tax favoured.

Single people, widows and widowers in that age group could even find that their marriage or remarriage prospects have soared.

They are the lucky ones who will qualify for the married couple's allowance for the rest of their lives when the tax benefit is abolished in April 2000 for those who have yet to reach 64.

The age-related married couple's allowance with its extra benefits starts when one of the partners reaches 65. But it does not matter how old the other spouse is. A 65-year-old woman could marry a man of 60, 30 or even younger - any legal marriage counts.

And it works the other way as well. From April 2000, there will be a unique tax incentive to fuel those tabloid stories of lonely old men picking up young mail-order brides in third world countries. Over 65s will be able to claim the married couple's allowance, which can be worth more than £500 per year in cash terms. It is the age of a partner rather than the age of the other or the date of the marriage which counts.

But John Battersby at accountants KPMG says that some people who may have calculated their future income and expenditure assuming they would keep the tax break will lose out. He says: "At the extreme, being born just a few minutes after midnight on April 6 1935, will lose up to £512 a year at present rates. And that's over £5,000 if you assume they live 10 years or £10,000 plus for those who survive for 20 years."

Although the Chancellor said he intended to help couples where at least one partner will be 65 or older by April 2000, many less well-off pensioner households could suffer.

The married couple's allowance for the over 65s is not a set cash sum but a percentage of earnings from pensions, savings and wages from any part-time work. To qualify for the allowance, pensioners and other older people must have the earnings to start with.

The changes in this year's budget which reduce the rate of tax relief on the married couple's allowance from 15 to 10 per cent could impact on the less well-off, although the Government has increased the slice of taxable income that qualifies for the marriage allowance. For many may not have enough earnings under the new rules to gain the full benefit.

In the current tax year - to April 5 - a married person aged over 65 pays no tax on the first £5,410 of earnings including her or his state pension. But the man in a married couple - Inland Revenue law is still sexist here - can claim an age-related married couple's allowance to cover the first £3,305 of his income. This can be transferred to his wife only if he has insufficient earnings and she has more.

Under the current age-related allowance rules, the first slice of taxable income is taxed at 5 per cent - the current 20 per cent rate less the 15 per cent married couple's allowance.

A man with the same income next year benefits from a £5,720 personal allowance and the new 10 per cent starting rate. But as the balance is then taxed at 23 per cent less the 10 per cent reduced married couple's rate, this taxpayer is around £30 worse off. Only the £80 increase to £100 in the winter allowance will stop this household's spendable income falling back, justifying Gordon Brown's claim that everyone is a winner.

A couple hit by higher tax bills would have more money to spend only if the husband had income he could transfer to his wife's personal allowance. But pensions and part-time earnings cannot be switched in this way.

Age-related allowances start to disappear once an income reaches £16,800 ( £16,200 in 1998-99) and will evaporate altogether for those earning more than £34,550. But all elderly couples keep the non-age related element of their relief - £1,970 in 1999-2000 which is the same as the allowance for the under 65s - no matter what their earnings. Even when the married couple's allowance for younger people goes in April 2000, the wealthiest over 65s will keep a protected £1,970 allowance at 10 per cent.

Two-thirds of all pensioners pay no tax, however.

Jobs & Money reader Betty Toull, aged 62, from London is outraged at the Chancellor's soundbite that pensioner couples will pay no tax until they earn around £15,000.

She says: "He's confusing pensioners with the over 65s all the way through. I'm a pensioner and I'm not 65 so I do not qualify."

To gain the maximum benefit, husband and wife must again ensure that their incomes are as evenly divided as possible. If one partner earns £15,000 and the other nothing, there will be a tax bill of around £1,200. The full text of the Chancellor's statement does make it clear, however, that both have to use their full personal allowance.

But that is not the only budget sound bite that is confusing. According to Simon Osborne at Child Poverty Action Group, most people believe the Minimum Income Guarantee for older people is a minimum pension payment. "It is not," he says. "It is a safety net, nothing more. It is part of income support, a means-tested benefit aimed at the very poorest. But the words means-test never appear in official speeches."

From next month, the minimum guaranteed will be £75 per week for a single pensioner. This compares with a minimum £73.30 for a younger disabled person claiming income support and £66.75 for the basic state pension. But savings of more than £8,000 mean an automatic rejection for income support.

Charities concerned with older people hope, however, that the Minimum Income Guarantee title will encourage the 700,000 pensioners that the Department of Social Security estimates should claim income support but do not, to come forward. This is nearly a third of the estimated 2.4 million pensioners who could claim.

Help the Aged says that claiming Income Support through the guise of the Minimum Income Guarantee can be the key to other worthwhile benefits.

Once you have established an entitlement to Income Support, you should receive help with council tax bills, receive housing benefit if you rent as well as receiving help with paying for dental care and glasses.

Age Concern says the poor take-up of means-tested benefits is a major issue. The Government has conducted local pilot studies to encourage more to sign up. But the results remain under wraps.

'Pulling wool over our eyes'

Retired driver Barry Maycock, from Alford, near Aberdeen, believes the minimum Income Guarantee is neither a guarantee nor a minimum income.

"It's an attempt to pull the wool over people's eyes," he says. "If you have anything much in savings or part-time income or a small occupational pension, it is a waste of time. You do not qualify."

Barry, aged 67, owned a small bus business until he retired. Now he drives children to school as a part-time job. His wife, Shirley, aged 63, works part-time in a local advice centre. They aim to stop paid work altogether next year.

Barry receives the state basic pension - the married rate is going up to £106.70 next month - plus an occupational pension worth around £10 a week.

"That takes us a few pennies a week over the guaranteed level but even if we did not have the pension, we would still not qualify," he says.

The Maycocks have a little saved - and are trying to put a little more away this year before stopping work. Income Support rules ensure that means-testing erodes payments once you have £3,000 and stop them altogether at £8,000.

Barry says these limits, unchanged for decades, imply you need to earn a 20 per cent return on your savings to make up for the loss.

"I started work in 1948 when the state basic pension started. The Government then said that you pay for older people and when you reach retirement, the younger generation will look after you. If they can hand out untaxed child benefit to all, they could give us a better basic pension without these gimmicks."

The Maycocks have a 935cc Daihatsu so they will benefit from lower road taxes on small cars. But higher petrol prices will wipe out that gain twice over for Barry, who needs to drive miles to the nearest big shops.